Blind Cave Fish

Blind Cave Fish (Astyanax mexicanus) are very interesting fish and one we’re proud to be able to share with you here at Blue Reef Aquarium Newquay. As the name suggests, these fish are blind, but this can vary in each subspecies. Also known as Mexican Tetras, these freshwater fish are commonly found in the lakes and streams of Mexico, Guatemala and the United States.

How to Identify a Blind Cave Fish

Silver in appearance, the Blind Cave Fish does not have the need for bright colours (attracting a mate) due to its inhibition of dark and murky waters. While they do not have eyes, you will be able to see ‘pockets’ where the eyes would typically be.

Interesting Blind Cave Fish Facts

There are plenty of interesting Blind Cave Fish facts to be aware of, many of which revolve around its vision. But this isn’t the only thing that makes them fascinating creatures. Explore some of the most interesting Blind Cave Fish facts below.

Why are Blind Cave Fish Blind?

On the surface, a fish being completely blind seems counterproductive, but what has ended up happening is they have adapted and become more efficient as a result. They have evolved to survive without their eyes/vision.

In order to conserve energy in environments where food is scarce, fish will evolve in order to survive and remove the chance of using energy where it is not necessary. The eyes and parts of the brain that process vision use up a lot of energy, so instead of wasting energy on this, the Blind Cave Fish focuses on ensuring its vital organs have enough energy to function. 

As the water they inhabit is typically murky and lacks much light, they would expel a lot of energy trying to use their vision. Instead, they have evolved to not need their vision and use this energy to hunt for food. This process is called pleiotropy, where the genes typically needed for eye development are reassigned to other areas, like increasing the number of taste cells for finding food.

What Do Blind Cave Fish Eat?

As we have mentioned before, the places Blind Cave Fish are found typically aren’t rife with food and sources of energy. They have therefore adopted a diet of generally whatever they can find. This includes worms, snails, other small fish, and insects. Being omnivorous, they also eat algae and other plant matter.

Where Do Blind Cave Fish Originate?

As the name Mexican Tetra suggests, you will commonly find these fish in Mexico, as well as Guatemala and the United States. They are quite hardy fish and are found in freshwater with temperatures between 20-25°c. 

There are actually two types of this species – one with eyes, one without. The one without inhabits dark, murky waters and doesn’t need its vision. The other is found in fast moving water and still requires its vision to navigate the waters.